Hello Everyone,
I have a capacitor in a 1935 Zenith 970A radio that I cannot identify. The pictures I have sent show a 2 1/8" long black capacitor with a red dot on it. One end connects to the candohm center terminal (ground) and the other connects to the 2nd audio tube #56. The capacitor has a reading of .005 when disconnected. If someone could give me the correct value for the capacitor I would appreciate it. Thank you.
Paul
First off, welcome to the Philco Phorum, a phamily phriendly Phorum phull of Philco phacts and phine pholks (See a pattern here?).
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Now to your radio.
The capacitor is identified as C10 on the schematic and is a cathode bypass capacitor for the triode 2nd AF (driver). It appears to be a 5uF 25V electrolytic capacitor. The 1st audio amp tube, also a 56 has the same size capacitor between its cathode and ground.
Considering the age of this set, I would definitely replace this and all electrolytic capacitors and all capacitors for that matter especially the cap across the plates of the 2 outputs and from the plate of one of the output tubes to ground. It is critical that the electrolytics be replaced because as they age, they either open (causing hum) or short (causing really bad things like blown rectifier tubes or worse, blown power transformers). Same with the plate bypass caps for the output stage.
The set has a radio-phono switch, according to the schematic, which makes it ideal for playing back old-time radio recordings off your computer, MP3, CD player, iPhone, etc. The amplifier in this set is no slouch. I suspect it is a Class AB 2 and may be good for as much as 10 watts or more.
Hope this helps
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That capacitor is either a .5 uf or a 5 uf, but I think it's 5 uf since it's rated at 25 volts, it looks like there are two C-10s and both are cathode bypass capacitors. That seems like a high value given the tubes they are connected to, I would have figured a .05 uf but I'm not familiar with brand Z.
Regards
Arran
Hello,
I would like to thank you gentlemen for the information. It appears that it is one of the 5uf capacitors in the set. I have sent a picture of a resistor that I also need identified. It appears to be a tubular wire wound type. One end is connected to the third pin of #58 I.F. tube (The first pin being the largest then counting clockwise the two small pins). The other end attaches to a small lug strip and a .02 400v capacitor. The resistor checks at 15.2K disconnected. Does this resistor identify as R15?
I believe that you are correct, that the resistor is R15, though the parts list shows it as being a 12,000 ohm resistor not a 15,000 ohm one. It's used to supply the screen grids of the tubes in the front end, and seems to be the only one listed as more then 1/2 a Watt on the parts list. This doesn't mean that the original wasn't changed, the parts list specs it at 2 Watts and most wire wounds are higher then that, if C4 shorted or became very leaky it would burn up R15 if it was a carbon resistor. I think that the orange resistor must be R14, it's supposed to be 30,000 ohms, and the cap next to it is likely C4 as they are connected in parallel, it's very likely an RF bypass.
Regards
Arran
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